You go to the Endurance to save Alex. Eventually you find him but the room is blocked off. You then have to clear the track the winch is on. First pull the winch towards the entrance to the room Alex is in:

Then jump to the ladder on the left side to push the winch to the right wall:

Then pull it backwards and jump on the right side to push the wench to the left wall. Now you can climb up to the maintenance hatch and clear the track:

To get the winch back so that it can clear the object blocking the room pull it backwards and jump on the left side. Then pull it towards the blocked off room again and you will have cleared the entrance.